Energy transfer from nucleic acids to Tb(III): Selective emission enhancement by single DNA mismatches

Enhanced luminescence resulting from energy transfer (EnT) from nucleic aci ds to Tb3+ has been utilized to investigate the binding of the ions to the bases and nucleotides, as well as in the detection of single mismatches in duplexes. Cytosine enhances the Tb3+ emission, but dCMP does not, indicatin g that the lanthanide bound to the phosphate group is too far away from the base for efficient energy transfer. Conversely, the enhancement of the Tb3 + luminescence by dGMP is greater than that of G, where the phosphate appea rs to aid in the binding of the ion to the base. We propose that the phosph ate group in dGMP is able to fold over and permit coordination of the ion t o the O6 and N7 atoms of the base while still bound to the anionic phosphat e oxygens, thus increasing the binding affinity and promoting efficient EnT . Single-stranded oligonucleotides greatly enhance the Tb3+ emission, but d uplexes do not. Single mismatches in the sequence of a duplex lead to selec tive luminescence enhancement in the presence of Tb3+. Th, largest enhancem ent was observed for the GG mismatch, followed by CA, GA, and CC, and the s mallest emission intensity was measured for TT and TG mismatches. The unexp ected role of adenine in the emission enhancement has been explained throug h preassociation of the Tb3+, thus permitting A to be in the coordination s phere of the ion. It was concluded that A is able to transfer energy to Tb3 + when bound to the ion, but in the absence of the supramolecular assembly, it cannot coordinate strongly enough to the lanthanide to effect EnT. The low emission enhancement by the TG mismatch has been explained in terms wob ble pair formation. These findings show that the enhanced emission of lanth anides can be successfully utilized to selectively detect single mismatches in duplexes.